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Development of a comprehensive database for materials with carbon-sequestering ability and how they perform in cement and geopolymer concrete
Development of a comprehensive database for materials with carbon-sequestering ability and how they perform in cement and geopolymer concrete
Concrete is the second most used material on earth after water. The main constituent of concrete is cement. Cement is essential for constructing any nation’s infrastructure, such as roads and bridges. However, the cement industry is responsible for a considerable share of the total anthropogenic CO2 emissions, about 8% (1). Additionally, OPC manufacturing causes significant environmental degradation as each 1 ton of cement requires 2.8 tons of raw materials (2) and generates about 1 ton of CO2 emissions. Therefore, the sustainability of construction material has been of high interest on both industry and research levels.
Several approaches have been adopted to ensure the sustainability of concrete, the most common of which has been to partially replace cement with supplementary cementitious materials (SCM). SCMs are mostly industrial byproducts, especially those with high silica and alumina content, such as fly ash. Those elements react with the cement hydration products and contribute further to the strength and durability of concrete.
Another approach has been to entirely eliminate cement and use geopolymer-based binders. Geopolymer is the product of alkali activation of aluminosilicate materials. Many researchers have considered it the most sustainable alternative for cement concrete (3). The source material can be natural such as rice husk ash, or industrial byproduct such as slag, fly ash, or ground glass fibers. The alkali activator can be either sodium hydroxide or sodium silicate, or a combination of both.
The construction industry has recently moved toward building materials that can absorb carbon from the atmosphere reducing CO2 concentrations. This characteristic can render a building or material carbon neutral (if not negative) over its service life. Several methods can facilitate carbon sequestering, and the most successful one has been mineral carbonation. In this method, the carbon from the atmosphere reacts with elements in the material. It then becomes chemically bound in cement or geopolymer concrete (primarily as mineral carbonate). Other studies have investigated carbon-sequestering biomass (biochar, bamboo, etc.) as fibers to reinforce the concrete and enhance the tensile strength.
Although several studies have investigated the carbon sequestering capacities of different materials (4–6), there has been no reliable database where you can get data on each material’s performance as a carbon sink if used as a cement replacement or as source material in geopolymer. Therefore, this proposal aims to test a wide range of materials for their capability of storing carbon as raw material first, then as bound material into cement or geopolymer systems. The database obtained from this investigation could be a vital tool to help the construction industry and the research community select suitable materials to fulfill both performance and sustainability.
To this purpose, a comprehensive literature review is to be carried out first to establish a good understanding of what materials have been investigated and how they performed as a carbon sink. After that, a list of all materials that can be a part of cement or geopolymer system should be prepared. The proposed experimental investigation, shown in the flowchart below, would include:
Material Characterization
1- The characterization of materials in terms of physical properties, including specific gravity and particle size distribution (Laser Diffraction).
2- The characterization of all materials in terms of chemical composition (XRD and XRF).
3- Thermogravimetric analysis (TGA) for all raw materials to use later to compare the degree of carbonation (the amount of calcium carbonate resulting from carbon curing).
Testing the capacity of absorbing carbon
1- Exposing all materials to carbon curing in a carbonation chamber at a selected pressure and duration.
2- Testing TGA again to determine the level of carbonation.
Testing the material in the cement paste system
1- Dosages of each material will be mixed with cement and water, and samples will be cured adequately for the test duration.
2- Carbonation testing should be carried out at selected ages of 1, 3, 7, 14, 28 days.
3- TGA should be performed on powdered samples obtained from the carbonated cement system samples to determine the level of carbonation.
4- TGA and Isothermal calorimetry should be performed to determine the pozzolanic activity of cement (ASTM C1897 (7)).
Testing the material in the geopolymer system
1- Dosages of 10N NaOH solution will activate each material.
2- TGA will be performed for each geopolymer product.
3- Carbonation testing should be performed.
4- TGA is to be conducted to evaluate the degree of carbonation.
5- TGA, SEM, and Isothermal calorimetry can assess the performance of each material as a geopolymer precursor at each dosage level of NaOH solution.
References
1. Mehta KP. Reducing the environmental impact of concrete. Concr Int. 2001;23(10):61–6.
2. Guo X, Shi H, Dick WA. Compressive strength and microstructural characteristics of class C fly ash geopolymer. Cem Concr Compos. 2010 Feb;32(2):142–7.
3. Salas DA, Ramirez AD, Ulloa N, Baykara H, Boero AJ. Life cycle assessment of geopolymer concrete. Constr Build Mater. 2018 Nov;190:170–7.
4. Gupta S, Kua HW, Low CY. Use of biochar as carbon sequestering additive in cement mortar. Cem Concr Compos. 2018 Mar;87:110–29.
5. Song X, Chen X, Zhou G, Jiang H, Peng C. Observed high and persistent carbon uptake by Moso bamboo forests and its response to environmental drivers. Agric For Meteorol. 2017 Dec;247:467–75.
6. Moon E-J, Choi YC. Carbon dioxide fixation via accelerated carbonation of cement-based materials: Potential for construction materials applications. Constr Build Mater. 2019 Feb;199:676–87.
7. ASTM International. ASTM C1897-20 Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements [Internet]. ASTM International; 2020 [cited 2021 Dec 28]. Available from: http://www.astm.org/cgi-bin/resolver.cgi?C1897-20
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